In a vehicle, the powertrain or powertrain system refers to the components that provide the power to move the vehicle. These components include the engine, transmission, drive/propeller shaft, differentials, and final drive. For an internal combustion engine, the engine combusts a fuel to generate mechanical power. This power rotates a crankshaft of the engine. The transmission receives the rotating crankshaft and manipulates the engine speed (i.e., the rotation of the crankshaft) to output a rotation speed of the drive/propeller shaft. The rotating drive shaft is received by a differential, which transmits the rotational power to a final drive to cause a movement of the vehicle. In an automobile, the differential enables the wheels, on a shared axle, to rotate at different speeds (e.g., during a turn, the outer wheel spins faster relative to the inner wheel to allow the vehicle to maintain its speed and line of travel). The final drive refers to the wheels, propeller, or other movement-producing device of the vehicle.
Because engine speed does not always equate to a desired final drive speed (and, consequently, vehicle speed), the transmission manipulates the engine speed to affect the drive shaft speed and, therefore, the desired vehicle speed. To achieve a different drive shaft speed relative to the engine speed, some transmission systems utilize a plurality of gears that either increase or decrease the drive shaft rotational speed relative to the engine speed using gear ratios (e.g., 2:1, which indicates that the engine is rotating twice as fast as the output speed). Gear selection can be done by an operator of the vehicle or automatically without operator input and can be based on engine speed, vehicle speed, throttle position, and load on the engine. For example, during highway driving, the transmission may use a higher gear that provides a relatively higher transmission output speed (i.e., speed of the propeller/driver shaft) than a lower gear to maintain/achieve the relatively greater vehicle speed needed for highway driving. As such, the transmission allows the vehicle to achieve desired vehicle speeds and powers largely independent of the engine.